1. Field of the Invention
The present invention provides a grinding machine wherein the coarse and fine grinding wheels are driven by a single rotating spindle, a wheel mount attached to the lower portion of the spindle containing the mechanism for moving the inner coarse wheel down to the workpiece relative to the stationary outer fine wheel.
2. Description of the Prior Art
U.S. Pat. No. 7,118,446, assigned to the assignee of the present invention, discloses a grinding assembly for shaping work pieces that includes one or more grind spindles, each of the grind spindles including two independent grinding wheels driven by the same spindle drive. The grind spindles translate horizontally to perform both edge and face grinding with a single grind spindle. A non-contact position sensor in a work spindle measures work spindle displacement during grinding and provides feedback to the grind spindle to regulate the force imparted on the work piece by the grind spindle.
The double spindle air bearing utilized in the '446 system mounts a stationary outer support structure, rotating spindle, and an inner concentric shaft. The rotating spindle is supported (inside) by the stationary outer support. The rotating spindle has an inner concentric shaft which is rotationally keyed to the spindle, but is allowed to move up and down. The up/down actuation is contained in the upper section of the rotating spindle/support structure. The fine grinding wheel is attached to the lower portion of the rotating spindle, and the coarse wheel is attached to the lower portion of the inner concentric shaft. The fine and coarse wheels rotate together since the inner concentric shaft and the spindle are keyed together rotationally. In the retract position, the coarse wheel is retracted up so the fine wheel can be used for grinding. In the extend position, the coarse wheel is extended out beyond the fine wheel so the coarse wheel can be used for grinding. The actuation of the inner coarse wheel is done by the inner concentric shaft of the spindle assembly. The cost of the spindle air bearing has increased dramatically and has prompted a design that is lower in cost and can be utilized in most grinder machines to increase throughput in a dual grind application (coarse and fine).